Indeed -- same position here. The trouble with developing Shopify apps is that your own application churn is additive with Shopify's. While that's the case with every platform, Shopify's churn rate is eye-wateringly high.
What you might be seeing a lot of these days is that app dev companies go around buying up other well-established apps and/or their development companies just because they can't find an app to make or get traction with apps they make at this point in the game. Even with great teams and money coming out their ears, they're having a hard time getting established with new apps.
There are 20 apps all doing the same thing competing with each other and all of them have had years head start, so having zero reviews compared to hundreds of favourable reviews can almost be insurmountable for a newcomer. Having said that, if you have 50 subscribers for your possibly obscure app, you can still eke out a good living.
Keep in mind there's a review process though, so just because you make it doesn't mean it will be published in their marketplace. Shopify tries hard to maintain an air of fairness but a large part of getting visibility with your app is who you know, too.
Re: "Keep in mind there's a review process though" - My experience of this is that Shopify wouldn't approve my App because there were existing Apps in their store which they thought were too similar.
So make sure it's sufficiently differentiable to existing Apps (no, I don't know what that means either!)
Some merchants on it are professionals and operate their business that way. Many merchants (and I don't have a percentage) are somewhere in the prosumer to wantrepreneur range and have unrealistic expectations.
Much of Shopify's strategy here, in developing a developer ecosystem, is to have developers effectively do technical support for its customer for free. I've troubleshooted (more times than I can count) theme, general platform, and other app issues. A while ago when Shopify was down after a merchant installed my app complained that I broke their Shopify store when in fact the entire Shopify platform was having a hiccup.